Question

where does the digestion start in human

Answer 1

Mouth as saliva start digesting when we chew food.

Answer 2

$\textbf{Mouth}$ is the place where digestion starts in human.

More to know?

$\textbf{Alimentary Canal }$:

The digestive system from Oesophagus to the anus is called alimentary canal. It is about 9 metre long. It is also called food tube.

It constitutes the organs namely :

Buccal cavity, Oesophagus, Stomach, Small intestine, Large intestine, Rectum, Anus.

$\textbf{Role of mouth }$:

Humans take in food through the mouth. It is the uppermost part of alimentary canal which is bounded by lips and cheeks, and contains tongue and slaivary gland. The food taken in is chewed or groinded by teeth at the same time in the salivary glands, saliva starts to secrete which contains enzymes( $\textbf{Salivary Amylase }$ )that breaks search into sugar.

Now the tongue helps in mixing this saliva with food, it also gives taste of food also it helps in swallowing the food.

$\textbf{Role of oesophagus}$ :

It is tubular part of alimentary canal about 25cm long. It is also the narrowest part of alimentary canal. It is hollow which allows the passage of food from Buccal cavity to the stomach. During which food gets mixed with various digestive juices.

$\textbf{Role of Stomach }$

It is J-shaped bag like structure made of muscle. Here gastric glance are present which secret mucus, HCL and digestive enzymes. The function of mucus is to protect stomach lining from the action of enzymes and acid. HCL kills bacteria present in food, making the food acidic; so that enzymes can act on it. Here food stays for 4-5 hours.

$\textbf{Role of Small intestine }$:

It is located below the stomach and is coiled in appearance. This tube is abour 7.5 m long. It has three main divisons : duodenum, jejunum and ileum. Duodenum is the first part having two different ducts namely bile duct and pancreatic duct. In this tube digested food (partially) is mixed with pancreatic juice, bile juice anf other juices. Jejunum is the middle pary, found only in man. Ileum is the last part of Small intestine.

Total absorbtion takes place in the ileum. This ileum has villi on its surface. This villi increases surface area for absorbtion. The villi have blood vessels, digested food passes villi passes to there and enters the blood stream. Which then transfers to liver and then to the heart.

$\textbf{Role of Large intestine, Rectum and Anus}$:

It is about 1.5 m long organ Food from small intestine moves here. Here the most of water and salt be removed from the water by the absorbtion. This intestine allow the passage of faecal matter through the anus.